For agriculture uses, mainly in dry-field farming, a disc-type operating machine is used at cultivation and stripe seeding of seeds. Since an operating machine having a cultivation disc is dragged by a towing vehicle such as a tractor, the cultivation disc is correspondingly rotated. At this time, the cultivation disc can perform works of making furrows, making a ridge between fields, and covering soils again after strewing seeds or fertilizer, and the like, for example. Herein, in order to support the rotation of the cultivation disc, a combination of a bearing and a housing, a rolling bearing such as a unitized ball bearing or tapered roller bearing or the like is usually used for one disc.
Since several to tens of discs are used in parallel for one disc-type cultivating machine so as to efficiently perform the works, several to tens of the bearings are also used. In such agriculture uses, the cultivating machine is basically used outdoors (fields) and is used for cultivation. That is, the cultivating machine is used under severe environments where it is exposed to water, mud, sand and the like.
As an example of the background art technology, Patent Document 1 discloses a hub bearing assembly, in which a bearing and a housing having a flange part are fitted with each other, and the flange part and a disc are coupled by a rivet. A hub shaft has a male screw on an outer periphery of a tip thereof, a sleeve has a female screw on an inner periphery thereof, and the hub shaft and the sleeve are screw-fixed. An outer periphery of the sleeve is in contact with an inner periphery of an inner ring of the bearing.
Further, as an example of a seal to be used for agriculture use, a bearing seal disclosed in Patent Document 2 may be exemplified. The bearing seal can be attached to an outer ring by an annular protrusion provided at an elastic member and can be attached to a circumferential groove formed on an inner periphery of an outer ring of the bearing by a snap operation.